The invention relates to a method for obtaining energy from wells yielding gas containing petroleum and more especially from submarine wells, and to equipment for performing the method.
Petroleum wells differ substantially as regards their product and the conditions of production. More importantly, there are differences as regards proportions of petroleum and natural gas and the pressure of the product from the well. The parameters relating to the product however vary during the course of operation of the well. These facts have to be taken into account carefully, more especially in the case of submarine wells, since it is hard to obtain access to the drilled well itself.
In the case of oil wells with a gage pressure it has so far been conventional to separate the product consisting of oil and gas, into its components on a platform arranged above the level of the sea. That is to say it is separated on such an offshore platform in a gas separation operation involving non-energetic pressure reduction.
Since it is not generally possible to assume that the underground pressure will be maintained during the entire time of production from the well sufficiently to convey the product to an offshore platform or to a station on shore it was necessary to devise a new method of production from submarine sources, in accordance with which the excess pressure at the well is reduced in a valve and the transport of the oil to the land takes place by driven machinery. The product may be transported just as it comes from the well, that is to say without separation into its components ("multiphase flow") or after separation into oil and gas ("single phase flow"), pumps being used for mixed products and for petroleum while for natural gas compressors are used.
The fact that in this system a large amount of electrical energy is required for the driven machinery involves high costs. It is also to be taken into account that the electrical power has to be supplied through heavy cables in view of the large amount of such power needed.